Urban Expansion: A Major Cause Of Forest Loss

Abstract

Urban expansion is increasingly recognised as a primary driver of forest loss across sub-Saharan Africa, with far-reaching consequences for biodiversity, climate regulation, carbon sequestration, and human well-being. This paper examines urban expansion as a major cause of forest loss in Asaba metropolis, Delta State, Nigeria, drawing on geospatial analysis of four epochs of Landsat satellite imagery spanning 1991 to 2021. Supervised Maximum Likelihood Classification (MLC) was applied to extract land use and land cover (LULC) data across six categories, while Normalized Difference Vegetation Index (NDVI), Normalized Difference Building Index (NDBI), Land Surface Temperature (LST), and Urban Heat Island (UHI) indices were computed to assess the spatial dimensions of urban-induced environmental change. Overall classification accuracy exceeded 97% for all epochs, with Kappa coefficients ranging from 0.92 to 0.98. Findings reveal that built-up area expanded from 0.91% of the total metropolitan land mass in 1991 to 26.56% in 2021, while vegetation cover declined from 18.19% to 8.83% over the same period. Farm land also contracted from 68.34% to 53.17%, confirming the compound nature of green land loss. NDBI values rose progressively from -0.18 to 0.17 in 1991 to 4.7 to 9.4 in 2021, while NDVI values contracted sharply to a range of -0.09 to 0.39 by 2021, indicating widespread vegetation degradation. Land surface temperature and urban heat island intensity also increased across the study period, reflecting the thermal consequences of reduced green cover and expanding impervious surfaces. Projections indicate that built-up area could reach approximately 51% of the metropolitan land mass by 2051 under current growth trajectories. The study concludes that urban expansion is a primary and ongoing cause of forest loss in Asaba metropolis and calls for integrated land use planning, green infrastructure policies, and strict enforcement of forest conservation regulations as essential steps toward sustainable urban development in peri-urban areas.